1. Field of Invention
This invention pertains to method and apparatus for providing a predictive visible indication of ranges of shades for colored material, including ranges of shades within prescribed tolerances and ranges of shades statistically anticipated for a prescribed production specification.
2. Related Art and Other Considerations
The concept of color space is useful in representing and modeling color phenomena. Color space is a three-dimensional space in which each point corresponds to a color, including both luminance and chrominance aspects. The tristimulus values R (red), G (green), and B (blue) form such a color space. As used herein, color space has three axes--L* (lightness); a* (red to green); and b* (blue to yellow). Tristimulus values are transformed (e.g., converted) into color space using, for example, the CIE 1976 L*a*b* equation. The CIE 1976 L*a*b* equation is explained in sundry prior publications including "CMC: Calculation of Small Color Differences For Acceptability", AATCC Technical Manual/1992, pp. 322-324.
In the production and/or use of colored materials, a color standard or specification is typically established for the material. It often occurs that the color standard can be achieved from a field of colorant formulations (e.g. a number of variations of colorant mixtures). Modern computer color formulation systems (including spectrophotometric instruments coupled with computers) have been used to find concentrations of a set of colorants which, when mixed together, achieve such color standards. These modern computer formulation systems typically use the well-known Kubelka-Munk mixing laws.
Realistically, colorants themselves (e.g., colorant concentrations) usually vary. Issues attending colorant variation are addressed in the thesis "Spectrophotometric Color Formulation Of Off Standard Colorants: Formula Selection With Respect to Match Sensitivity And The Optimization of Colorant Formulation With Respect To Colorant Availability", of Michael Keating in 1986. The Keating thesis provides a model for optimizing an existing colorant formulation with respect to colorant availability and develops an index of "sensitivity", whereby a match of colorants can be chosen based on the relatively sensitivity of the match to changes in the concentrations of the colorants. The Keating thesis proposes an analytical method which determines parameters (e.g., shape, position, etc.) of an n-dimensional ellipse which describes sensitivity and optimized vectors of concentrations.
SheLyn Incorporated has developed a color control system which utilizes the Keating thesis. The SheLyn color control system predicts the performance (production pattern) of a given color formulation. As exemplified by FIG. 11, screen graphics and printed output of such a color control system provides a display of expected production variation of the formula against a CMC acceptability ellipsoid for that shade.
The Keating thesis and SheLyn color control system deal only with colorant formulation, other factors such as stability and fading characteristics explicitly being beyond the scope of the prior Keating research. Yet, in many industrial applications, subsequent treatment of colored materials affects not only lightness, but also produces a color shift. Often a series of treatment steps or operations are required in route to a finished material. Generally a color standard is established with respect to the finished product.
One non-limiting example of such subsequent treatment occurs in textile production, particularly the manufacture of denim. As is well known, denim is typically produced using a dyed warp yarn extending in a first direction, and an uncolored fill yarn which extends in a cross direction. Upon being woven with the warp yarn and fill yarn, the unwashed denim is called "rigid" denim. The denim is then subjected to one or more washing operations at a laundry. The number and nature of the washing operations is dependent upon the desired commercial characteristics of the denim. The washing operations can include (for example), in consecutive order, a rinse stage, a stonewash stage, an instant old stage, new age stage, and bleachout stage.
A denim consumer (e.g., a blue jean manufacturer) generally establishes a color standard for the consumer's product. For example, if a blue jean manufacturer produces a stonewash denim jean, the manufacturer will provide a color standard for the stonewash denim jean.
For quality control purposes, the color standard is typically in the form of a visual shade band or blanket. With respect to denim, the visual shade blanket is usually produced in a manner such as the following: the laundry washes, to the pre-selected stage (e.g., stonewash, instant old, etc.), between one thousand and five thousand garments, cut from three or more rolls of sample denim. From these garments the laundry cuts and submits to the denim customer a range of swatches of differing coloration. The customer chooses a center swatch representing the preferred or ideal coloration, as well as other tolerance swatches which illustrate acceptable extremes of coloration. In some cases the swatches may then be mounted (e.g., in juxtaposition) on a substrate to form a blanket.
After adoption of the color standard (e.g., production of the center and tolerance swatches), during denim production the color standard is used periodically for quality control at the laundry. For example, if, after reaching the desired washing stage at the laundry, a new batch of denim does not fit within the visual shade band represented by the blanket, the laundry must stop production and submit samples of the new batch to the denim consumer for approval. In view of such facts as variation between the shade range of production denim and the sample denim used for the shade blanket, as well as differences in concentration/formulation of dye for the warp yarn, the scenario of submission to the customer may repeat several times during the life of a product. Unfortunately, each such stoppage occasions delay, as well as increased inventory and downtime at the laundry.
The inefficiency of the current denim production/laundry quality control regime is exacerbated as customers demand not only higher quality denim, but denim of greater diversity (e.g., colorations diverse from conventional indigo, denim of differing character), all with shorter production lead times.
Lacking in the prior art, among other things, is a system which provides the colored material (e.g., denim) consumer with a visible indication or prediction for the potential of long term shade variation before the colored material goes into production.
Present techniques allow for color variation in order to achieve an image depicting physical characteristics or desired aesthetic modifications to a material design. For example, U.S. Pat. No. 4,500,919 to Schreiber (incorporated by reference) discloses a system in which a color original is generated by taking into consideration aesthetically desired alterations.
U.S. Pat. No. 4,954,976 to Noonan, entitled "Method For Simulating Dyed Fabric" (incorporated herein by reference), provides a simulated view (via color monitor or hardcopy) of dyed fabric. Noonan fails, among other things, to take into consideration variable shade ranges at differing stages of processing. Rather, Noonan uses color correction (e.g., shading) at edges of yarn shape to simulate the travel of yarn over and beneath other yarns. In particular, Noonan corrects colors of simulated yarn shape so that the average color is equal to the spectrophotometrically measured color of the actual yarn shape. Thus, Noonan provides no suggestion for providing simulation of shade ranges of fabric, much less shade ranges at varying stages of processing.